HDMCS.co

What is it?

It's a mod (duh) that allows the use of skins with a higher resolution than the default 64x64 (64x32 in the pre-1.8 format)

How do I use it?

Install Forge (If you don't know, google it)

Install the mod (drop it in the /mods/ folder)

IMPORTANT! While you're in the .minecraft folder, go to /assets/skins and delete everything there. Why? Because Minecraft 1.8 caches skins and if you don't clear this cache, it won't download you new HD skin!

Be aware that this is a beta build, and some features don't work all the time.
For example: Skins load reliably most of the time, but player heads don't. When placed normally they work most of the time, but certain ones won't. Known offenders are the "Hats" on servers like Hypixel